Microglia are ……… in origin

Options

A. endodermal
B. mesodermal
C. ectodermal
D. both (1) and (3)

Answer

To determine the origin of microglia, we will analyze the options provided and understand the developmental biology behind these cells.

### Step-by-Step Solution:

1. **Understand the Options**: The options given are:
- Endodermal
- Mesodermal
- Ectodermal
- Both 1 and 3

2. **Define Germ Layers**:
- **Ectoderm**: The outermost germ layer, which develops into structures such as the skin and nervous system.
- **Mesoderm**: The middle germ layer, which gives rise to muscles, bones, and the circulatory system.
- **Endoderm**: The innermost layer, which forms the lining of the gut and associated organs.

3. **Identify the Origin of Microglia**:
- Microglia are a type of glial cell found in the central nervous system. They are involved in immune defense in the brain.
- Microglia originate from primitive hematopoiesis in the yolk sac during embryonic development.

4. **Determine the Correct Option**:
- Since microglia arise from the yolk sac, which is associated with mesodermal development, the correct answer is that microglia are **mesodermal in origin**.

5. **Final Answer**: The correct option is **Mesodermal**.